The present invention relates to a precursor fiber bundle for manufacture of carbon fibers, a production apparatus thereof, and a method for manufacturing a carbon fiber bundle. Particularly, the present invention relates to a series of precursor fiber bundles for manufacture of carbon fibers, composed of at least two fiber bundles each of which comprises 30,000 or more filaments and which fiber bundles are joined each other at the terminal end of one and the starting end of the other one directly or through an intervening fiber bundle, a production apparatus thereof, and a method for manufacturing a carbon fiber bundle using the series of precursor fiber bundles for manufacture of carbon fibers. The series of precursor fiber bundles for manufacture of carbon fibers is stabilized to make a stabilized fiber bundle which is further carbonized to make a carbon fiber bundle.
Carbon fibers have been used as reinforcing materials of aircraft and sporting goods. Recently, carbon fibers begin to be used also as architectural and civil engineering materials and reinforcing materials for members of energy related apparatuses, and such demands are growing rapidly. To meet these demands and furthermore to further increase the demands, carbon fibers having at least conventional properties and less expensive than the conventional carbon fibers are being demanded.
To supply less expensive carbon fibers to the market, the production cost of carbon fibers must be lowered. One method for reducing the cost is to heat-treat (stabilizing and carbonizing) a precursor fiber bundle for manufacture of carbon fibers which fiber bundle has far more filaments than before, for improving the productivity of carbon fibers.
However, if the number of filaments in a precursor fiber bundle increases, i.e., if the filament density becomes higher, heat accumulation in the precursor fiber bundle during stabiizing treatment performing in an oxidizing atmosphere (air) tends to be large. As a result, the filaments are likely to generate heat, and the oxidation reaction of filaments in the stabilizing treatment tends to run away.
So, where the filament density is higher, the stabilizing temperature in the stabilizing treatment must be set at a level lower than that in the stabilizing treatment of a precursor bundle having lower filament density, to take a longer time for the stabilizing treatment, in order to prevent the filament breaking due to the runaway reaction.
However, if the stabilizing treatment temperature is lowered greatly, the stabilizing treatment time becomes too long, and it can happen that the productivity of stabilizing treatment is not improved even though the filament density is higher.
On the other hand, the stabilizing treatment process comprises the steps of continuously supplying a series of precursor fiber bundles from the inlet of a stabilizing treatment furnace into the furnace, stabilizing it in the furnace, to produce a stabilized fiber bundle, and continuously taking out the stabilized fiber bundle from the outlet of the furnace. The precursor fiber bundle continuously supplied into the stabilizing treatment process must be a series of precursor fiber bundles formed by joining a plurality of precursor fiber bundles at the terminal end of one and the starting end of another, each of which bundles is wound around bobbins or spools or contained in cans with a certain limited length.
However, where precursor fiber bundles having a high filament density are simply joined each other, the filament density at the joined portion becomes very higher than the filament density at the other portions (main bundle portions). Simply, the filament density becomes double. Therefore, in the stabilizing treatment, the oxidation reaction of filaments at the joined portion tends to run away compared to the main bundle portion.
A method for splicing or joining precursor bundles is described in Japanese Patent Publication (Kokoku) No. 53-23411. In this method, precursor fiber bundles are spliced each other at the mating ends into a series of precursor fiber bundles, and the series of precursor fiber bundles are treated to be stabilized. Then, the joining portion of the series of stabilized fiber bundles is cut off and removed, and each of the bundles are re-spliced into a series of stabilized fiber bundles and treated to be carbonized.
Japanese Patent Laid-Open (Kokai) No. 54-50624 describes a method of applying a flame resistant compound such as silicone grease to the joining portions.
Furthermore, Japanese Patent Laid-Open (Kokai) No. 56-37315 describes a method comprising heat-treating the ends (the starting end and the terminal end) of precursor fiber bundles and then the precursor fiber bundles are spliced each other by a specific splicing method.
Moreover, Japanese Patent Laid-Open (Kokai) No. 58-208420 describes a method for interlacing the terminal end of one precursor fiber bundle and the starting end of another precursor fiber bundle by a high speed fluid.
However, in any of these methods, since the filament density at the joining portion becomes very higher than that of the main bundle portion, burning, breaking, etc. of filaments are likely to be caused by the heat accumulation during stabilization treatment.
Japanese Patent Publication (Kokoku) No. 60-2407 describes intervening stabilized fibers or carbon fibers at the splicing portion for inhibiting the heat accumulation. However, since the square knot is used for the joining portion, the knot is tightened and the filament density becomes higher. So, the heat accumulation inhibiting effect is small.
As a method for improving these disadvantages, Japanese Patent Publication (Kokoku) No. 1-12850 describes interlacing precursor fiber bundles with each other or interlacing a precursor fiber bundle with a stabilized fiber bundle.
FIG. 1 is a perspective view showing an example of the method. In this method, the mating ends 2a and 2b of the fiber bundles to be joined are simply overlaid in the form of the bundles as they are, inserted into an interlacing treatment chamber 4 of a fluid interlacing nozzle 1, relaxed by about 5 to 60%, and treated by a high speed fluid jetted from two nozzle holes 3 for interlacing the filaments at both ends 2a and 2b with each other. The method for joining with an intervening of a stabilized fiber bundle has an effect that the heat accumulation at the joining portion makes small compared to the direct joining of precursor fiber bundles since the stabilized fibers little generate heat in the stabilizing process.
As for the fluid interlacing nozzle used in this conventional method, as shown in FIG. 1, the high speed jets injected from the two nozzle holes 3 installed in the small entangling treatment chamber 4 collide with each other in the interlacing treatment chamber 4, to produce turbulent flow which opens the fiber bundles for interlacing the filaments with each other. This method is effective for fiber bundles small in the number of filaments constituting them.
However, if the number of filaments constituting each of the fiber bundles to be joined is very large, the jets injected from the nozzle holes do not hit all the filaments of the fiber bundles, and the fiber bundles are not interlaced at filament level and it remarkably happens interlacing between sub-bundles of filaments each other. Such interlaced sub-bundles of filaments occur unevenly at the joining portion and portions with high filament densities are locally formed, and heat is likely to be accumulated there.
An interlacing based on several interlaced sub-bundles of filaments is weak in joining strength since interlacing strength between filaments is weak. The examples described in Japanese Patent Publication (Kokoku) No. 1-12850 disclose only fiber bundle comprising up to 12,000 filaments. If precursor fiber bundles each of which comprises 30,000 or more filaments handling in the present invention are joined at their mating ends directly or through an intervening stabilized fiber bundle according to the known method, breakage of filaments and burning out of filaments due the accumulation of heat occur for the reasons described above.
In addition, in the case of precursor fiber bundles having a high filament density, as the case may be, it may be necessary to impart crimps to the fiber bundles for intensifying the integrity between filaments for better handling convenience in continuously taking out the bundles from their stored condition. Since the crimped fiber bundles are bulky and have their filaments slightly entangled with each other, it is difficult to join the mating ends of the crimped precursor fiber bundles by using the method described in Japanese Patent Publication (Kokoku) No. 1-12850.
That is, even if crimped fiber bundles are overlaid and treated by a high speed fluid, the fiber bundles cannot be sufficiently opened compared to noncrimped fiber bundles since they are crimped. Furthermore, being crimped, the fiber bundles are bulky, cottony and likely to be inhibited in the movement of filaments, and interlacing at filament level is not sufficient compared to non-crimped fiber bundles. Therefore, compared to non-crimped fiber bundles, the filaments are less uniformly entangled with each other at the joining portion, and the joining strength at the joined portion becomes low.
In view of the above problems, the object of the present invention is to provide a continuous precursor fiber bundle for manufacture of carbon fibers, comprising two thick fiber bundles respectively having 30,000 or more filaments and joined each other at their mating ends directly or through an intervening fiber bundle, with the filaments of both the fiber bundles interlaced with each other at the joined portion, and also to provide a production apparatus thereof.
Another object of the present invention is to provide a method for manufacturing a carbon fiber bundle comprising stabilizing the continuous precursor fiber bundle and further carbonizing.
The precursor fiber bundle for manufacture of carbon fibers, the production apparatus thereof, and the method for manufacturing a carbon fiber bundle using the precursor fiber bundle, respectively of the present invention to achieve the above objects are as follows.
The following inventions A1 through A6 are included in the precursor fiber bundle for manufacture of carbon fibers of the present invention respectively.
Invention A1
A precursor fiber bundle for manufacture of carbon fibers, comprising a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, a second precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, and an intervening fiber bundle comprising many filaments having non-exothermic property at stabilizing treatment temperature, wherein the terminal end of said first fiber bundle and the starting end of said second fiber bundle are joined through said intervening fiber bundle; and at a first joined portion where the terminal end of said first fiber bundle and the starting end of said intervening fiber bundle are joined and at a second joined portion where the starting end of said second fiber bundle and the terminal end of said intervening fiber bundle respectively, the filaments in the respective fiber bundles are substantially uniformly interlaced with each other.
Invention A2
A precursor fiber bundle for manufacture of carbon fibers according to A1, wherein the intervening fiber bundle comprises a stabilized fiber bundle.
Invention A3
A precursor fiber bundle for manufacture of carbon fibers according to A2, wherein a relation of 0.4xc3x97Gxe2x89xa6Fxe2x89xa61.5xc3x97G is satisfied where F is the number of filaments of the stabilized fiber bundle and G is the number of filaments of each of the precursor fiber bundles for manufacture of carbon fibers.
Invention A4
A precursor fiber bundle for manufacture of carbon fibers according to any one of A1 through A3, wherein the filaments of each of the precursor fiber bundles for manufacture of carbon fibers have crimps and the crimps are removed at the joined portions.
Invention A5
A precursor fiber bundle for manufacture of carbon fibers, comprising a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments and a second precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, wherein the terminal end of said first fiber bundle and the starting end of said second fiber bundle are directly joined, and the filaments in the respective fiber bundles are substantially uniformly interlaced with each other at a joined portion where the terminal end of said first fiber bundle and the starting end of said second fiber bundle are joined.
Invention A6
A precursor fiber bundle for manufacture of carbon fibers according to A5, wherein said filaments of each of the precursor fiber bundles for manufacture of carbon fibers have crimps, and the crimps are removed at the joined portion.
The following inventions B1 through B6 are included in the apparatus for producing the precursor fiber bundle for manufacture of carbon fibers of the present invention respectively.
Invention B1
An apparatus for producing a precursor fiber bundle for manufacture of carbon fibers, comprising
(a) a first fiber bundle holding means for holding the flatly opened terminal end of a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, in the transverse direction of the terminal end, at least at two positions apart from each other in the longitudinal direction,
(b) a second fiber bundle holding means for holding the flatly opened starting end of a second precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, in the transverse direction of the starting end, at least at two positions apart from each other in the longitudinal direction,
(c) an intervening fiber bundle holding means for holding the flatly opened starting and terminal ends of an intervening fiber bundle comprising many filaments having non-exothermic property at stabilizing treatment temperature, in the transverse direction of the starting and terminal ends, at least at two positions apart from each other in the longitudinal direction,
(d) a first interlacing treatment means for interlacing the filaments each other at the terminal end of said first fiber bundle and the starting end of said intervening fiber bundle, and
(e) a second interlacing treatment means for interlacing the filaments each other at the starting end of said second fiber bundle and the terminal end of said intervening fiber bundle, wherein
(f) said first fiber bundle holding means and said second fiber bundle holding means are provided in such a manner that the tip of the terminal end of said first fiber bundle and the tip of the starting end of said second fiber bundle are subjected to face each other, and
(g) said intervening fiber bundle holding means is provided in such a manner that the intervening fiber bundle is subjected to overlap with said first fiber bundle held by said first fiber bundle holding means and said second fiber bundle held by said second fiber bundle holding means.
Invention B2
An apparatus for producing a precursor fiber bundle for manufacture of carbon fibers according to B1, wherein the first interlacing treatment means and the second interlacing treatment means are filament interlacing treatment means using fluid respectively.
Invention B3
An apparatus for producing a precursor fiber bundle for manufacture of carbon fibers according to B1, wherein the first interlacing treatment means and the second interlacing treatment means are filament interlacing treatment means using a needle punch respectively.
Invention B4
An apparatus for producing a precursor carbon fiber bundle for manufacture of carbon fibers, comprising
(a) a first fiber bundle holding means for holding the flatly opened terminal end of a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, in the transverse direction of the terminal end, at least at two positions apart from each other in the longitudinal direction,
(b) a second fiber bundle holding means for holding the flatly opened starting end of a second precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, in the transverse direction of the starting end, at least at two positions apart from each other in the longitudinal direction, and
(c) an interlacing treatment means for interlacing the filaments each other at the terminal end of said first fiber bundle and the starting end of said second fiber bundle, wherein
(d) said first fiber bundle holding means and said second fiber bundle holding means are provided in such a manner that said first fiber bundle held by said first fiber bundle holding means and said second fiber bundle held by said second fiber bundle holding means are subjected to overlap with each other.
Invention B5
An apparatus for producing a precursor fiber bundle for manufacture of carbon fibers according to B4, wherein the interlacing treatment means is filament interlacing treatment means using fluid.
Invention B6
An apparatus for producing a precursor fiber bundle for manufacture of carbon fibers according to B4, wherein the interlacing treatment means is filament interlacing treatment means using a needle punch.
The following inventions C1 through C16 are included in the method for manufacturing the carbon fiber bundle of the present invention.
Invention C1
A method for manufacturing a carbon fiber bundle, comprising
(a) a step of overlaying the flatly opened terminal end of a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments and the flatly opened starting end of an intervening fiber bundle comprising many filaments having non-exothermic property, and substantially uniformly interlacing the filaments of both of the fiber bundles with each other to form a first joining portion,
(b) a step of overlaying the flatly opened starting end of a second precursor fiber bundle for manufacture of-carbon fibers, having 30,000 or more filaments and the flatly opened terminal end of said intervening fiber bundle, and substantially uniformly interlacing the filaments of both of the fiber bundles with each other to form a second joining portion,
(c) a step of treating to stabilize a continuous precursor fiber bundle for manufacture of carbon fibers formed with said first and second fiber bundles which are joined through said intervening fiber bundle at said first and second joining portions, to obtain a stabilized fiber bundle, and
(d) a step of treating to carbonize said stabilized fiber bundle, to obtain a carbon fiber bundle.
Invention C2
A method for manufacturing a carbon fiber bundle according to C1, wherein the intervening fiber bundle comprises a stabilized fiber bundle.
Invention C3
A method for manufacturing a carbon fiber bundle according to C2, wherein a relation of 0.4xc3x97Gxe2x89xa6Fxe2x89xa61.5xc3x97G is satisfied where F is the number of filaments of the stabilized fiber bundle of the intervening fiber bundle and G is the number of filaments of each of the precursor fiber bundles for manufacture of carbon fibers.
Invention C4
A method for manufacturing a carbon fiber bundle according to any one of C1 through C3, wherein means for forming the first and second joining portions comprise filament interlacing means using fluid respectively.
Invention C5
A method for manufacturing a carbon fiber bundle according to C4, wherein when the first and second joining portions are formed, a density of each of the fiber bundles overlapping to form the first and second joining portions is 4,000 filaments/mm or less.
Invention C6
A method for manufacturing a carbon fiber bundle according to C5, wherein where filaments in the first and second fiber bundles have crimps, the crimps of the filaments at the terminal end of the first fiber bundle and the starting end of the second fiber bundle are removed before forming the first and second joining portions.
Invention C7
A method for manufacturing a carbon fiber bundle according to any one of C1 through C3, wherein means for forming the first and second joining portions comprise filament interlacing means using a needle punch respectively.
Invention C8
A method for manufacturing a carbon fiber bundle according to C7, wherein when the first and second joining portions are formed, a density of each of the fiber bundles overlapping to form the first and second joining portions is 4,000 filaments/mm or less.
Invention C9
A method for manufacturing a carbon fiber bundle according to C8, wherein where filaments in the first and second fiber bundles have crimps, the crimps of the filaments at the terminal end of the first fiber bundle and the starting end of the second fiber bundle are removed before forming the first and second joining portions.
Invention C10
A method for manufacturing a carbon fiber bundle, comprising
(a) a step of overlaying the flatly opened terminal end of a first precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments and the flatly opened starting end of a second precursor fiber bundle for manufacture of carbon fibers, having 30,000 or more filaments, and substantially uniformly interlacing the filaments of both of the fiber bundles with each other to form a joining portion,
(b) a step of treating to stabilize a continuous precursor fiber bundle for manufacture of carbon fibers formed with said first and second fiber bundles which are joined at the joining portion, to obtain a stabilized fiber bundle, and
(c) a step of treating to carbonize said stabilized fiber bundle, to obtain a carbon fiber bundle. Invention C11
A method for manufacturing a carbon fiber bundle according to C10, wherein means for forming the joining portion comprises filament interlacing means using fluid.
Invention C12
A method for manufacturing a carbon fiber bundle according to C10, wherein means for forming the joining portion comprises filament interlacing means using a needle punch.
Invention C13
A method for manufacturing a carbon fiber bundle according to C11 or C12, wherein when the joining portion is formed, a density of each of the fiber bundles overlapping to form the joining portion is 4,000 filaments/mm or less.
Invention C14
A method for manufacturing a carbon fiber bundle according C13, wherein where filaments in the first and second fiber bundles have crimps, the crimps of the filaments at the terminal end of the first fiber bundle and the starting end of the second fiber bundle are removed before forming the joining portion.
Invention C15
A method for manufacturing a carbon fiber bundle according to C13 or C14, wherein after forming the joining portion and before the stabilizing treatment, a stabilization inhibitor is applied to the joining portion.
Invention C16
A method for manufacturing a carbon fiber bundle according to C15, wherein the stabilization inhibitor is boric acid water.
In the present invention, as the filaments constituting the precursor fiber bundles for manufacture of carbon fibers, filaments of an acrylic polymer conventionally used for production of carbon fibers is preferably used.
In the present invention, the filaments constituting the precursor fiber bundles for manufacture of carbon fibers may have crimps or have no crimp. If the filaments have crimps, it is preferable that a crimping degree of each of the filaments is 8 curls/25 mm to 13 curls/25 mm. When a precursor fiber bundle for manufacture of carbon fibers is joined with an intervening fiber bundle or another precursor fiber bundle for manufacture of carbon fibers, it is preferable that the crimps of the filaments are removed at a joining portion of the fiber bundles. It is preferable that a removal of the crimps is achieved by heat-treating the end of the fiber bundle.
In the present invention, the expression that the filaments of the intervening fiber bundle have non-exothermic property at stabilizing treatment temperature means that the calorific value obtained according to the DSC (differential scanning calorimeter) method at the stabilizing treatment temperature is 500 cal/g or less, and the detail will be described later.
As the intervening fiber bundle comprising many filaments having non-exothermic property at the stabilizing treatment temperature, a stabilized fiber bundle subjected to a stabilizing treatment, particularly a stabilized fiber bundle obtained by stabilizing a fiber bundle formed by acrylic polymer filaments at a temperature of 200xc2x0 C. to 350xc2x0 C. in air is preferably used.
In the present invention, the expression that the filaments are substantially uniformly interlaced with each other means that the many filaments constituting one fiber bundle and many filaments constituting another fiber bundle are individually interlaced with each other at single filament level, and does not mean interlacing between one group having several filaments and another group having several filaments.
In the present invention, a filament interlacing treatment means using fluid or a needle punch is preferably used as the filament interlacing treatment means for substantially uniformly interlacing filaments with each other at the joining portion formed between the end (the terminal end or the starting end) of a precursor fiber bundle and the end (the starting end or the terminal end) of an intervening fiber bundle, or at the joining portion formed between the end (the terminal end) of a precursor fiber bundle and the end (the starting end) of another precursor fiber.
It is preferable that the stabilizing treatment temperature for the precursor. fiber bundles for manufacture of carbon fibers in the present invention is 200xc2x0 C. to 350xc2x0 C.
Giving a stabilization inhibitor before stabilizing treatment, to the joining portion in one continuous precursor fiber bundle for manufacture of carbon fibers obtained by directly joining the mating ends of the precursor fiber bundles for manufacture of carbon fibers is intended to prevent burning and breaking of filaments likely to be caused by the heat accumulation at the joining portion during stabilizing treatment. As the stabilization inhibitor, boric acid water is preferably used.